Or, any benefits of getting AV are speculative, but destroying Clegg’s career is an immediate payoff:
It seems to me that the AV system itself is highly unattractive, that all the possible benefits which might accrue as a result of it are really quite speculative and far-future things, with very considerable potential to go wrong (after all, the implementation of AV in Australia 93 years ago does not seem to have generated much momentum toward a more proportional system).
The benefit of destroying Nick Clegg’s political career, however, seems reasonably immediate and certain, and the possibility of putting an end to the Liberal Democrats as a party looks achievable enough to be worth a try. I don’t actually think it’s necessarily irrational at all to vote No out of Clegg-hate.